1/4 pound (1 stick) unsalted butter, room temperature
1/2 cup plus 2 tablespoons sugar
1 large egg, separated
1 teaspoon pure vanilla extract
1 1/4 cups all-purpose flour
1/4 teaspoon coarse salt
1/2 cup whole blanched almonds
1/2 cup jam, or preserves
Preheat oven to 350 degrees. In the bowl of an electric mixer fitted with the paddle attachment, beat together butter and 1/2 cup sugar on medium speed until light and fluffy, about 3 minutes. Add egg yolk and vanilla; beat well. Whisk together flour and salt, and add to mixture, beating on low until combined.
In a small food processor, combine almonds with remaining 2 tablespoons sugar, and process until almonds are finely ground. In a small bowl, lightly beat egg white. Form dough into 1-inch balls. Dip in egg white, then in almond-and-sugar mixture. Place balls on parchment-lined baking sheet. Make a deep indentation in the center of each ball with your finger or bottom of a thick wooden spoon.
Bake for 10 minutes, remove from oven, and press down the
centers again. Fill the center of each cookie with about 1 teaspoon of jam. Rotate sheets, and bake until golden brown, 10 to 12 minutes more. Remove from oven, and place on a wire rack to cool.